LOSS AND LOSS ADJUSTMENT RESERVES - (Schedule of Cumulative Paid Losses and ALAE, Net of Reinsurance Recoverable) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Claims Development [Line Items]
Unfavorable loss and LAE reserve	$ 296,230	$ 230,515	$ 158,110	$ 97,706
Homeowners [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	764,998
Unfavorable loss and LAE reserve	102,279
Homeowners [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	27,015	27,049	26,982	26,927	$ 26,831	$ 26,462	$ 26,007	$ 24,657	$ 23,095	$ 15,047
Homeowners [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	30,449	30,376	29,739	29,092	27,984	26,886	24,730	21,350	14,052
Homeowners [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	26,287	25,982	25,580	24,047	22,723	21,323	19,250	11,119
Homeowners [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	26,777	26,113	25,186	23,923	23,120	20,728	13,693
Homeowners [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	37,473	35,803	35,123	33,867	31,606	19,986
Homeowners [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	60,555	59,722	57,891	53,831	37,033
Homeowners [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	90,415	86,647	79,359	52,214
Homeowners [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	148,274	142,716	102,556
Homeowners [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	176,580	135,589
Homeowners [Member] | Accident Year 2018 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	141,173
Homeowners [Member] | All outstanding liabilities for unpaid claims and ALAE prior to 2009, net of reinsurance
Claims Development [Line Items]
Unfavorable loss and LAE reserve	138
Commercial General Liability [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	53,261
Unfavorable loss and LAE reserve	18,888
Commercial General Liability [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	12,377	11,308	10,454	10,130	8,593	8,046	7,384	6,466	4,236	2,253
Commercial General Liability [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	7,918	7,631	7,382	7,238	6,363	5,553	3,855	2,279	1,187
Commercial General Liability [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	6,349	5,831	4,866	4,246	3,673	3,366	2,763	764
Commercial General Liability [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	4,098	3,841	3,686	3,342	2,632	1,714	871
Commercial General Liability [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	5,033	4,606	3,867	3,366	2,233	882
Commercial General Liability [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	5,130	4,375	3,855	2,593	717
Commercial General Liability [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	3,827	3,249	2,296	798
Commercial General Liability [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	5,088	3,657	1,515
Commercial General Liability [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	2,478	1,592
Commercial General Liability [Member] | Accident Year 2018 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	963
Commercial General Liability [Member] | All outstanding liabilities for unpaid claims and ALAE prior to 2009, net of reinsurance
Claims Development [Line Items]
Unfavorable loss and LAE reserve	1,416
Personal Auto Liability [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	62,834
Unfavorable loss and LAE reserve	4,374
Personal Auto Liability [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	242	243	243	243	243	241	225	220	218	$ 61
Personal Auto Liability [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	3,037	3,035	2,984	2,978	2,942	2,863	2,715	2,482	$ 1,713
Personal Auto Liability [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	2,755	2,755	2,755	2,726	2,644	2,562	2,381	$ 1,417
Personal Auto Liability [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	1,444	1,430	1,393	1,384	1,333	1,293	$ 867
Personal Auto Liability [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	2,112	2,109	2,069	1,906	1,609	$ 907
Personal Auto Liability [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	4,291	4,122	3,678	3,120	$ 1,455
Personal Auto Liability [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	2,807	2,670	2,293	$ 1,393
Personal Auto Liability [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	23,053	17,258	$ 8,084
Personal Auto Liability [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	20,762	$ 12,821
Personal Auto Liability [Member] | Accident Year 2018 [Member]
Claims Development [Line Items]
Cumulative paid, claims and allocated claim adjustment expenses, net of reinsurance	2,331
Personal Auto Liability [Member] | All outstanding liabilities for unpaid claims and ALAE prior to 2009, net of reinsurance
Claims Development [Line Items]
Unfavorable loss and LAE reserve	$ 9